If you've bought moissanite and wondered whether it would fool a diamond tester — or if you're a buyer worried about whether a "diamond" is actually moissanite — this is the article you need.
The short answer: it depends entirely on which tester is used.
A basic thermal diamond tester? Moissanite often reads as diamond. A modern dual-function tester? It gets flagged as moissanite. Neither answer alone is the complete truth, and the confusion between these two realities is what produces most of the misinformation online about moissanite being "deceptive."
Here's exactly what's happening.
How Diamond Testers Actually Work
Before understanding what moissanite does, you need to understand how diamond testers work.
Thermal conductivity testers — the most common type, and what most people mean when they say "diamond tester" — work by applying a small amount of heat to the stone's surface and measuring how quickly it dissipates. Diamond is one of the best thermal conductors on earth, far better than glass, cubic zirconia, or most other simulants. When heat dissipates quickly, the tester reads "diamond."
Electrical conductivity testers work on a different principle. Diamonds are electrical insulators — they don't conduct electricity. Moissanite, by contrast, has slight electrical conductivity. A tester that measures electrical resistance can use this difference to distinguish moissanite from diamond.
Dual-function testers combine both measurements. They're more expensive, less portable, and far more accurate. Most casual buyers and non-specialist jewelers use thermal-only testers. Gemological labs and experienced diamond dealers use dual-function equipment.
Moissanite and Thermal Testers: Yes, It Often Passes
Here's the fact that surprises most people: moissanite has exceptionally high thermal conductivity. Not as high as diamond — diamond runs roughly 1,000–2,000 W/(m·K), while moissanite sits around 500–600 W/(m·K) — but high enough that many basic thermal testers read moissanite as diamond.
This is not a flaw or a fraud. It's simply a physical property of silicon carbide, which is what moissanite is made of. The stone dissipates heat faster than almost every other diamond simulant, which is why it behaves so differently from cubic zirconia or glass on a thermal tester.
The practical result: if a jeweler or buyer tests your moissanite with a basic thermal tester — the kind that looks like a pen with a metal probe — it may well read "diamond." This has caused genuine confusion in jewelry stores, and it's why some moissanite owners have had jewelers tell them their stone "tested as diamond."
"I took my moissanite to a local jeweler just out of curiosity, and the tester said diamond. The jeweler seemed as surprised as I was." — Community member, r/Moissanite
This experience is common and expected. It's not fraud. It's physics.
Dual-Function Testers: Moissanite Gets Flagged
The second half of the story is equally important.
Modern multi-function testers — priced higher and used by more sophisticated buyers and gemologists — measure electrical conductivity alongside thermal conductivity. Diamond is an excellent electrical insulator. Moissanite is slightly conductive.
A tester measuring both properties will correctly identify moissanite as "not diamond." Some testers output a separate "moissanite" reading rather than simply "not diamond" — making the distinction explicit.
"The newer dual testers are specifically designed to flag moissanite. Any jeweler using up-to-date equipment will know immediately what they're looking at." — Discussion from r/Moissanite
One important caveat: as moissanite manufacturing has advanced, some stones now have very low electrical conductivity — approaching diamond's near-zero level. Industry research notes that discriminating "weak conductors from a good insulator like diamond, using a portable battery-operated device, is difficult, and even the best available testers cannot do it reliably" at the highest resistance levels. This is an edge case for most buyers, but it illustrates why no portable tester is a perfect diamond identifier. Only full gemological analysis — including spectroscopy — provides definitive identification.
What This Means for You as a Moissanite Buyer
If you're buying moissanite — or already own it — here's what the diamond tester situation actually means in practice:
You are not being deceived. When a thermal tester reads your moissanite as diamond, it's working exactly as designed. Thermal testers were built to distinguish diamonds from cubic zirconia and glass — not from moissanite, which didn't exist as a commercial product when most of these testers were developed.
A jeweler saying "it tested as diamond" doesn't mean your moissanite is a diamond. Reputable jewelers know this. Any gemologist with current knowledge will test with a dual-function tester or use a loupe to check for the double refraction moissanite shows — something diamond doesn't.
If you want to verify your moissanite is genuine moissanite (and not CZ), a dual-function tester is the right tool. CZ fails even the basic thermal test.
Your GRA or moissanite grading certificate is more reliable than any tester. Buy from a reputable seller who provides documentation, and keep it.
What Diamond Testers Cannot Tell You
Diamond testers — of any kind — have meaningful limitations beyond the moissanite question:
- They cannot tell you the quality of a diamond (cut, clarity, color, carat)
- They cannot reliably distinguish all natural diamonds from all lab-grown diamonds
- They can give false readings based on temperature, metal settings, or probe contact angle
- They are not substitutes for gemological grading by an independent lab (GIA, IGI, AGS)
For moissanite specifically: the double refraction test is more reliable and requires no equipment. Looking through the stone at a 45-degree angle with a loupe shows doubled facet edges — something diamond doesn't show. Any experienced jeweler knows this check immediately.
FAQ: Moissanite and Diamond Testers
Will moissanite pass a diamond tester?
On a basic thermal conductivity tester, moissanite often reads as diamond because of its high thermal conductivity. On a dual-function tester that also measures electrical conductivity, moissanite is typically identified separately from diamond.
Why does moissanite fool diamond testers?
Moissanite (silicon carbide) has unusually high thermal conductivity — similar to diamond's — which is what basic diamond testers measure. It dissipates heat much faster than glass or cubic zirconia, triggering a positive reading on thermal-only testers.
Can a jeweler tell moissanite from diamond without a tester?
Yes. An experienced jeweler identifies moissanite through double refraction — moissanite shows doubled facet edges when viewed at an angle under a loupe. Diamond is singly refractive and doesn't show this. This visual check is fast, reliable, and requires no equipment beyond a loupe.
What kind of tester correctly identifies moissanite?
A dual-function tester measuring both thermal and electrical conductivity can distinguish moissanite from diamond. Moissanite has slight electrical conductivity; natural diamond does not.
Does moissanite passing a thermal tester mean it's fake?
No. Moissanite is a real gemstone — silicon carbide that occurs naturally (extremely rarely) and is commercially produced in labs. It is not a fake diamond. The fact that it shares thermal properties with diamond is a characteristic of the stone, not an indication of fraud.
Should I get my moissanite certified?
If you bought from a reputable seller, you typically receive a GRA or similar certificate. This document is a more reliable indicator of what you have than any portable tester result. Keep it with your jewelry.
Can moissanite pass as diamond at a pawn shop?
A pawn shop using only a basic thermal tester may not immediately distinguish moissanite from diamond. However, experienced appraisers typically use dual-function testers or apply the double refraction check. Attempting to sell moissanite as diamond is fraud regardless of testing outcomes.
The bottom line: moissanite passes basic thermal diamond testers because of its genuine physical properties — high thermal conductivity. It does not pass more sophisticated dual-function testers designed to detect electrical conductivity differences. Neither outcome is surprising once you understand how the testers work.
For everyday moissanite buyers, none of this changes the value of the stone. Moissanite is not pretending to be diamond. It's a distinct gemstone with its own properties — including ones that happen to make basic diamond testers behave unexpectedly.
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Research from gemological sources and r/Moissanite community discussions.
